541 research outputs found

    Teleparallelism: A New Insight Into Gravity

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    Teleparallel gravity, a gauge theory for the translation group, turns up as fully equivalent to Einstein's general relativity. In spite of this equivalence, it provides a whole new insight into gravitation. It breaks several paradigms related to the geometric approach of general relativity, and introduces new concepts in the description of the gravitational interaction. The purpose of this chapter is to explore some of these concepts, as well as discuss possible consequences for gravitation, mainly those that could be relevant for the quantization of the gravitational field.Comment: Chapter to appear in "Handbook of Spacetime", edited by A. Ashtekar and V. Petcov (Springer, Berlin, 2013). V2: misprints corrected, references update

    On the monoid of partial isometries of a cycle graph

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    Funding Information: This work is funded by national funds through the Foundation for Science and Technology (FCT), I.P., under the scope of the projects UIDB/00297/2020 and UIDP/00297/2020 (NovaMath - Center for Mathematics and Applications). Publisher Copyright: © TÜBİTAKIn this paper we consider the monoid DPCn of all partial isometries of an n-cycle graph Cn. We show that DPCn is the submonoid of the monoid of all oriented partial permutations on an n-chain whose elements are precisely all restrictions of a dihedral group of order 2n. Our main aim is to exhibit a presentation of DPCn. We also describe Green’s relations of DPCn and calculate its cardinality and rank.publishersversionpublishe

    Treatment and energy valorisation of an agro-industrial effluent in upflow anaerobic sludge reactor (UASB)

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    The accelerated growth of the population brings with it an increase in the generation of agro-industrial effluents. The inadequate discharge of these effluents significantly affects the quality of water resources. In this way, it becomes important to invest in treatment processes for agro-industrial effluents, particularly low-cost ones. In this context, the present study includes the design and construction of an UASB reactor and optimization of the anaerobic digestion treatment of the raw effluent from sweet chestnut production in the agro-industrial company Sortegel. The efficiency of the system was evaluated through the determination / monitoring of oxygen chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS), biogas production rate and quality (% methane). The reactor was fed for 25 weeks and operated under mesophilic conditions (temperature 30-40 °C). Different values were tested for the hydraulic retention time (HRT) and volumetric flow rate (VF): 0.66 days (VF=1509 L.m-3.d-1); 1.33 days (VF=755 L.m-3.d-1); 2.41 d days (VF=415 L.m-3.d-1). The average COD removal efficiency reached values of 69%, 82% and 75%, respectively, and simultaneously the associated BOD5 removal efficiency was 84%, 91% and 70%. As regards TSS, removal values were 78%, 94% and 63%. In addition, high methane production rates were obtained, between 2500 and 4800 L CH4.kg-1 COD removed d-1. For all the hydraulic retention times tested, high concentrations of methane in the biogas were recorded: 66-75%, 70% and 75% for HRT of 0.66, 1.33 and 2.41 days, respectively.info:eu-repo/semantics/publishedVersio

    Anaerobic digestion performance in the energy recovery of kiwi residues

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    World production and trade of fruits generate losses in the harvest, post-harvest, handling, distribution and consumption phases, corresponding to 6.8% of total production. These residues present high potential as a substrate for the anaerobic digestion process and biogas generation. Thus, the energy valuation of the agro-industrial residues of kiwi production was evaluated by anaerobic digestion, aiming at optimizing the biogas production and its quality. Ten assays were carried out in a batch reactor (500 mL) under mesophilic conditions and varying a number of operational factors: different substrate/inoculum ratios; four distinct values for C: N ratio; inoculum from different digesters; and inoculum collected at different times of the year. The following parameters were used to control and monitor the process: pH, alkalinity, volatile fatty acids (VFA), volatile solids (VS) and chemical oxygen demand (COD). Among the tests performed, the best result obtained for the biogas production corresponded to the use of 2 g of substrate and 98 mL of inoculum of the anaerobic digester of the Wastewater Treatment Plant (WWTP) of Bragança, with addition of 150 mg of bicarbonate leading to a production of 1628 L biogas.kg-1 VS (57% methane). In relation to the biogas quality, the best result was obtained with 20 g of substrate and 380 mL of inoculum from the anaerobic digester sludge of WWTP of Ave (with addition 600 mg of sodium bicarbonate), presenting a value of 85% of CH4, with a production of 464 L biogas.kg-1 VS.This work was financially supported by: Project POCI-01-0145-FE DER-006984 – Associate Laboratory LSRE-LCM funded by FEDER through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) – and by national funds through FCT – Fundação para a Ciência e a Tecnologia.info:eu-repo/semantics/publishedVersio

    Commutative nilpotent transformation semigroups

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    Funding Information: This work is funded by national funds through the FCT\u2014Funda\u00E7\u00E3o para a Ci\u00EAncia e a Tecnologia, I.P., under the scope of the projects UIDB/00297/2020 and UIDP/00297/2020 (Center for Mathematics and Applications). The third author is funded by national funds through the FCT\u2014Funda\u00E7\u00E3o para a Ci\u00EAncia e a Tecnologia, I.P., under the scope of the studentship 2021.07002.BD. We thank the referee for their careful reading of the paper and their many helpful comments and suggestions. The authors are also thankful to Ricardo P. Guilherme for his helpful comments. Publisher Copyright: © The Author(s) 2024.Cameron et al. determined the maximum size of a null subsemigroup of the full transformation semigroup T(X) on a finite set X and provided a description of the null semigroups that achieve that size. In this paper we extend the results on null semigroups (which are commutative) to commutative nilpotent semigroups. Using a mixture of algebraic and combinatorial techniques, we show that, when X is finite, the maximum order of a commutative nilpotent subsemigroup of T(X) is equal to the maximum order of a null subsemigroup of T(X) and we prove that the largest commutative nilpotent subsemigroups of T(X) are the null semigroups previously characterized by Cameron et al.publishersversionpublishe

    As mulheres nos movimentos sociais de moradia: a cidade sob uma perspectiva de gênero

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    O presente trabalho propõe-se a analisar questões relacionadas à presença de mulheres organizando, participando e liderando movimentos sociais populares que reivindicam moradia. Verifica-se que tal presença é acentuada nessas formas de organização e, diante deste fato, serão levantadas hipóteses de fatores que influenciem essa participação. O principal fator a ser considerado são as relações sociais provenientes da divisão sexual do trabalho, cuja reprodução reserva socialmente às mulheres o espaço privado – ou seja, o espaço do lar –, a partir da imposição do trabalho doméstico e de cuidados ao sexo feminino. Também será apontado como a participação das mulheres nos movimentos populares contribui para seu empoderamento e de que maneira isso pode refletir no planejamento de políticas públicas voltadas às mulheres

    A inovação na empresa solidaria enquanto estrategia de entrada e sustentabilidade no mercado

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    Orientador: Divonzir Lopes BellottoMonografia(Graduação) - Universidade Federal do Paraná,Setor de Ciências Sociais Aplicadas, Curso de Ciências Econômica

    Tratamento e valorização energética de efluente agroindustrial em reator UASB (Upflow Anaerobic Sludge Blanket)

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    O acelerado crescimento da população traz consigo um aumento na geração de efluentes agroindustriais. A descarga inadequada desses efluentes afeta significativamente a qualidade dos recursos hídricos. Dessa forma, torna-se imperioso investir em processos de tratamento dos efluentes agroindustriais, em particular processos de baixo custo. Nesse contexto, o presente estudo compreende a concepção e construção de um reator UASB e otimização do tratamento por digestão anaeróbia do efluente bruto da produção de castanha pela empresa agroindustrial Sortegel. A eficiência do sistema foi avaliada mediante a determinação/monitorização dos parâmetros Carência Química de Oxigênio (CQO), Carência Bioquímica de Oxigênio (CBO5), Sólidos Suspensos Totais (SST), taxa de produção e qualidade (% de metano) do biogás. O reator foi alimentado durante 25 semanas e operado em condições mesofílicas (temperatura 30-40ºC). Foram testados diferentes valores para o tempo de retenção hidráulica (HRT) e caudal volumétrico (QV): 0,66 d (QV=1509 L.m-3.d-1); 1,33 d (QV=755 L.m-3.d-1); 2,41 d (QV=415 L.m-3.d-1). A eficiência média de remoção de CQO alcançou valores de 69%, 82% e 75%, respetivamente e, simultaneamente, a eficiência de remoção de CBO5 associada foi de 84%, 91% e 70%. Relativamente ao teor de SST, os valores de remoção foram 78%, 94% e 63%. A taxa de produção de metano situou-se entre 2500 e 4800 L.CH4.kg-1 CQO removido d-1. Para o conjunto dos tempos de retenção hidráulico testados, foram registadas elevadas concentrações de metano no biogás gerado: 66 - 75%, 70% e 75% para HRT de 0,66, 1,33 e 2,41 dias, respetivamente.info:eu-repo/semantics/publishedVersio

    Valorização energética do glicerol através da digestão anaeróbia

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    Mestrado com dupla diplomação com a Universidade Tecnológica Federal do ParanáA fim de diminuir a dependência dos combustíveis fósseis e cumprir a legislação Europeia, o consumo de biodiesel tendo vindo a aumentar significativamente. A produção desse combustível gera como subproduto o glicerol, que em excesso no mercado pode ter impacto até no valor comercial do biodiesel. Apesar do glicerol ser utilizado para outros fins industriais, o seu teor de impurezas limita o seu processamento. A digestão anaeróbia do glicerol é uma alternativa que vem sendo estudada para sua valorização através da geração de metano. A carga do glicerol (1800 g CQO.L-1) pode provocar um stresse cinético que acarreta a inibição dos microrganismos metanogénicos. Dessa forma, esse trabalho teve como objetivo principal testar alternativas de pré-tratamentos com ultrassons e exposição a microrganismos, utilizando o Aspergillus niger e Escherichia coli e posterior digestão anaeróbia do glicerol. Inicialmente num digestor batch de mistura completa (500 mL), foram utilizadas na alimentação concentrações de glicerol de 0,2, 1,7 e 3,2%, testados diferentes tempos de exposição do glicerol a ultrassons (3 a 15 h) e degradação prévia do glicerol por microrganismos Aspergillus niger e Escherichia coli. Os melhores resultados foram replicados em um reator Upflow Anaerobic Sludge Blanket (UASB) de 16,5 L de volume útil. O reator UASB apresentou um Tempo de Retenção Hidráulico (TRH) de 11,5 d. Com alimentação em contínuo com carga orgânica de: (A) 0,34 kg CQO.m-3.d-1 (semana 1-3); (B) 0,34 kg CQO.m-3.d-1 + 15 h de ultrassons (semana 4-5); (C) 1,56 kg CQO.m-3.d-1 (semana 6-8); (D) 1,56 kg CQO.m-3.d-1 + A. niger (semana 9-10). Os melhores resultados no reator batch foram obtidos para a concentração de 0,2% de glicerol e 15 h de ultrassons, obtendo-se 77% de metano e uma produção de 1153 L CH4.kg-1 de glicerol; para concentração de 1,7% de glicerol com A. niger, o volume gerado foi de 117 L CH4.kg-1, a que correspondeu uma qualidade do gás de 65% de metano. Para a concentração de 3,2% verificou-se uma inibição em todos os ensaios experimentais. No reator UASB, o pré-tratamento com ultrassons (B) permitiu obter 4000 L CH4.kg-1 glicerol e o A. niger (D) proporcionou uma produção de 1000 L CH4.kg-1. O valor energético do biogás gerado, no pré-tratamento com ultrassons evidenciou um aumento de 43% no valor agregado (5,8 €.kg-1 glicerol) e 87% (306 €.kg-1 SV) face ao ensaio sem pré-tratamento, enquanto que o pré-tratamento com o A. niger proporcionou um aumento de 4 vezes na produção de metano (101 €.kg-1 SV). Os valores mais elevados da remoção de CQO (60 - 69%) e ST (74%), bem como a menor concentração de ácidos carboxílicos no material digerido (88 g.L-1), correspondem igualmente ao ensaio experimental mais favorável (B). No processo de digestão anaeróbia em ambos os ensaios, batch e em contínuo, foi registada a formação de ácidos carboxílicos (oxálico, propiónico e glutárico). A utilização do A. niger no pré-tratamento favoreceu a formação de lípase, o que resultou na produção máxima de ácido glutárico, 325 mg.L-1 na semana 10. A produção de ácido oxálico ocorreu durante todo o período experimental, com maiores concentrações para alimentação de 1,56 kg CQO.m-3.d-1, variando entre 11 e 13 mg.L-1, a que correspondem as menores produções de metano.In order to reduce the dependence on fossil fuels and comply with European legislation the consumption of biodiesel is increasing significantly. The production of this fuel generates glycerol as by-product, whose excess in the market can influence the commercial value of biodiesel. Although glycerol is used for several industrial purposes, the impurity content of the residual glycerol limits its processing. The anaerobic digestion of glycerol to produce energy through the generation of methane is an alternative for its valorization. The high organic load of crude glycerol (1800 g-1 COD.L-1) can cause kinetic stress that leads to the inhibition of methanogenic microorganisms. Thus, this work had as main objective to test alternative pre-treatments of the reactor feed with ultrasound and microorganisms, namely, Aspergillus niger and Escherichia coli prior to the anaerobic digestion of glycerol. Initially it was performed tests using a continuous stirred-tank reactor in batch operation (500 ml), with glycerol concentrations of 0.2, 1.7 and 3.2%, pre-treated by sonication for different times (3 to 15 h) and by previous degradation with either A. niger or E. coli microorganisms. The best performance in the batch reactor was observed for glycerol concentration of 0.2% sonicated for 15 h, which yielded 77% of methane with a production of 1153 L CH4.kg-1. A good performance was also obtained with glycerol concentration of 1.7% pretreated with A. niger with 65% yield of methane and production of 117 L CH4.kg-1. The glycerol concentration of 3.2% resulted in inhibition in all experimental trials. The best conditions were replicated in an Upflow Anaerobic Sludge Blanket Digestion (UASB) reactor, with volume of 16.5 L. The UASB reactor had a Hydraulic Retention Time (HRT) of 11.5 d. The feeding was carried out with an organic load of: (A) 0.34 kg COD.m-3.d-1 (week 1-3); (B) 0.34 kg COD.m-3.d-1 + 15 h ultrasound (week 4-5); (C) 1.56 kg COD.m-3.d-1 (week 6-8); (D) 1.56 kg COD.m-3.d-1 + A. niger (week 9-10). The experiments were also done without the pre-treatments for comparison. In the UASB reactor, the feed pre-treated with ultrasound resulted in a methane yield of 4000 L CH4.kg-1 glycerol and the feed pre-treated with A. niger, a methane yield 1000 L CH4.kg-1 glycerol. Calculation of the energetic value of the biogas generated showed that the ultrasound pre-treatment provided a 43% increase in the value added of the residual glycerol (5.8 €.kg-1 glycerol) and 87% (306 €.kg-1 VS). Whereas the pre-treatment with A. niger provided 4 times the production of methane (1.6 €.kg-1 glycerol and 101 €.kg-1 VS). The highest methane yields occurred with 1.56 kg COD.m-3.d-1 and pre-treatment with ultrasound for 15 h (B). This result was confirmed by the higher removals of COD (60-69%) and ST (74%), also by to the lower concentration of carboxylic acids in the digested material, which amounted to 88 g.L-1. The formation of the oxalic, propionic and glutaric acids was observed in both UASB and batch reactors. The use of A. niger in pre-treatment favored lipase formation, which resulted in the maximum amount of glutaric acid observed of 325 mg.L-1 at week 10. The production of oxalic acid was observed during the whole sampled period for the higher feed concentration of 1.56 kg COD.m-3.d-1, with variable amounts in the range between 11 and 13 mg.L-1, when lower methane yields were recorded. The highest propionic acid production was observed for the higher feed load of 0.34 kg COD.m-3.d-1, in which the phosphorus consumption was higher compared to the same load treated with ultrasound.POCI-01-0145-FEDER-006984 -Laboratório Associado LSRE-LCM - financiado pelo Fundo Europeu de Desenvolvimento Regional (FEDER), através do COMPETE2020 – Programa Operacional Competitividade e Internacionalização (POCI) e por fundos nacionais através da Fundação para a Ciência e a Tecnologia
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